Method of and apparatus for cleaning coal



Feb. 15,1938. N. D. LEVIN METHOD OF AND APPARATUS FOR CLEANING COAL Original Filed Oct. 11, 1934 ATT'Y 6 Sheets-Sheet 1 VENTOR! //'/5 D. Lev/n,

Feb. 15, 1938. N. 'D. LEVIN METHOD OF AND APPARATU FOR CLEANING COAL 6 Shets-Sheet 2 Original Filed Oqt. 11, 1934 [NVE/YTOFP: N/Ys D.Le v/n,

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METHOD OF AND APPARATUS FOR CLEANING COAL briginal Filed Oct. 11, 1934 wzj irmm I ATT'X MENTOR .m v b 0 N Patented Feb. 15, 1938 ING COAL

Nils n. Levin, Columbus, Ohio, assignor to The Jeflrey Manuiaoturingcompany, a corporation of Ohio Application October 11, 1934, sews... 147,901 Renewed July 31, 1937 12 Claims. (Cl. 209-173) My invention relates to the separation of materlals according to their specific gravities and the re-clainiing of the solid constituents of the separating medium, and one of the objects of my invention is the provision of an improved method of separating coal from its impurities by increasing the efficiency of operation.

Another object of the invention is to provide improved apparatus for reclaiming the solidconstituents oi the separating medium for gravity separation of impurities from coal.

A further object of the invention is the pre liminary treatment of raw coal or run of mine coal for gravity separation of impurities from the coal employing insoluble material mixed with water so that when such coal impurities are removed from the separating medium a minimum amount 01' such solid constituents wili'be taken out or said medium.

A further object of the invention is the provision of a system of coal cleaning apparatus method therewith to reduce the expense of operation to a minimum by enabling the use of insoluble granular materials in their natural states and without comminution, in the separating medium, and in the washing of the separated coal reclaiming such solid materials as. may adhere thereto upon emerging from the separating medium.

Other objects of the invention will appear hereinafter, the novel features and combinations being set forth in the appended claims.

In the accompanying drawings,

Figs. 1 and 2, placed end to end, illustrate apparatus including" a separating tank for cleaning coal and for washing the same successively in a series of washing tanks;

Fig. 3 illustrates apparatus including a tank for immersing the raw coal or run of mine coal Fig. 6 is a diagrammatic plan view of the apparatus shown in Fig. 5, connected to a mixing tank, supply tank and settling tanks;

Fig. '7 is diagrammatic view illustrating conveying apparatus which may be used for removing sediment from the settling tanks shown in either Fig. 4 or Fig. 6;

Fig. 8 is a diagrammatic elevational view of the system shown in Fig. 4, to illustrate the relative elevations of the various tanks;

Fig. 9 is a wiring diagram to illustrate the automatic float control of lthe pump for replenishing water in the washing tanks; and A Fig. 10 is a curve illustrating a method of adapting a separating medium which will retain a, maximum amount of its solid constituents, so as frame ii on which are mounted the separating tank i2 and the series of washing tanks it, it and I5. The raw or run of mine coal may be introduced into the hopper l6, as shown in Fig. 1, in the bottom of which the discharge of the coal is regulated by the vertically slidable gate 11. The separating medium, comprising natural clay and granular sand in its natural state mixedwith water and an electrolyte, as hereinafter more fully explained, may be of varying depth in the tank I! according toconditions. The impurities which sink in the separating medium are received by the conveyor l8 comprising the flights i9, i9. These flights are adapted to travel in the direction of the arrow to convey the impurities, such as slate, to the chute 28 from which such impurities are delivered to the endless belt conveyor The coal which is capable of floating on a separating medium in the separating tank i2 is crowded toward the left, as-viewed in' Fig. 1, by the incoming raw coal, and such separated coal is received by the conveyor 23, comprising the flights M, M. The cleaned coal is conveyed upwardly along an incline in the direction of the arrow where it is discharged into the tank 23 in which a deflector plate 26' guides the coal to the conveyor 2i comprising the flights 23, 2t.

Inasmuch as the washing tank It is filled with water, the cleaned coal will tend to sink therein and consequently it is desirable to provide an inclined plate 29 for the flights 28 so that coal which reaches the plate 29 may be scooped from the semi-circular receiving portion 3% to move upwardly along the incline in the direction of washing apparatus in the direction of the arrow At the right-hand end of Fig. 1 is shown in dotted lines the position that the operating electric motor 31 occupies on that side of the frame II remote from the sprocket chain gearing 38 which is connected to simultaneously drive all of the conveyors shown in Figs. 1 and 2. The motor 31 is connected by reduction gearing 39 and the sprocket gearing 40 to that end of the shaft 4I remote from the sprocket chain 38. That is to say, the driving connection from the motor 37 is to one end of the shaft 4|, and to the opposite end of the latter is connected the endless sprocket chain 38 which in turn is connected to all of the traveling conveyors to drive them simultaneously. At the upper left-hand end of Fig. 2 is shown an inlet port 42 and at the bottom of the washing tanks I3, I4, and I5 are shown drain pipes 43, 44, and 45. Inasmuch as the separating medium in the separating tank I2 contains natural clay and sand in its natural granular state mixed with water and a very small quantity of electrolyte, a small quantity of the separating medium will adhere to the cleaned coal which is transferred by the conveyor 23 to the tank I3. When the conveyor 21 operates to transfer the coal to the next tank I4, most of the clay and sand is washed from the coal and dispersed in the water in the tank I3 where it settles on the conical bottom so that it mayfiow through the outlet port 43.

If any clay and sand still remain on the coal when introduced into the tank I3, further washing occurs and the clay and sand may be withdrawn through the port 44, shown in Fig. 2. Still further washing may occur in the tank I5 and the clay and sand eliminated through the outlet port 45. Clean water may be introduced intermittently and continuously through the port 42 for flow into the tank- I5 and thence into the tank I4 and from the latter into the tank I3. The upper edges 46 and 41 of the walls or separating partitions 48 and 49 are at lower elevations than the upper edges 50 and 5| of the end walls 52 and 53. Consequently, when the tank I5 is filled it may overflow the edge 46 into the tank I4, and when the latter is filled it may overflow the edge 41 into the tank I3.

Regulation of the flow of the sediment from the conical bottoms of the tanks I3, I4 and I5 through the outlet ports 43, 44, and may be secured by means of the system diagrammatically illustrated in Fig. 6. Manual valves 54, 55, and 56 may be placed in the pipes which lead from the ports 43, 44, and 45 so that each of the tanks I3, I4 and I5 may be individually drained to such an extent as to remove the sediment from the conical bottoms thereof. When any one of the valves 54, 55, 56 is opened the mixture of sediment and water will flow into the pipe 57 which is connected by the branch pipes 58 and 59- to the settling tanks and BI. The latter are at lower elevations than the bottoms of the sedimentation tanks I 3, I4, and I5, and flow thereto is controlled by the manual valves 62 and 53.

It is preferred to employ two settling tanks 60 and 6I so that one may be used for se me ation while the other is being used for receiving material from any one or more of the tanks I3, I4, I5. For instance, if the valve 82 is closed and the valve 83 is open the tank 84 may be used for sedimentation. During operation of the coal cleaning apparatus including the washing mechanism, it is preferred to close the valves 55 and 56 and regulate the'opening of the valve 54 so that as the clay and sand settle in the bottom of the tank I3 it will flow immediately into the settling tank 8|, the liquid in the tank I3 being automatically replenished by means of the pump 34 operated by the electric motor under the control of switch mechanism. When the pump 64 operates, the valve 56 is closed and the valve 61 is opened so that water will be withdrawn from the tank 80 into the pipe 42 for flow into the tank I5. After clear water has been obtained by sedimentation in the tank 6|, the valve 62 may be opened, the valve 63 closed, the valve 65 opened and the valve 51 closed. Then when the pump 54 operates, clear water will be withdrawn from the tank 6| through the pipe 68 into the pipe 42 and thence into the tank I5.

In Fig. 6, 69 designates a mixing tank in which the clay, sand, electrolyte and water may be thoroughly intermixed while the valve III is closed. It is desirable to effect this mixture in a separate mixing tank so that it may be permitted to age by standing in a quiescent condition for a period of approximately twenty-four hours, thereby rendering the electrolyte more eflicient in its efiect on the clay and sand con-' stituents.

After the separating medium has been aged for a predetermined period of time, the valve I0 may be opened to permit the mixture to flow into the storage or supply tank II which is larger in capacity than the tank 59, and from which the medium may flow into the separating tank I2 under the control of the manual valve I2.

In the system illustrated in Fig. 4, mixing and storage tanks are provided as indicated at I3 and I4 which are connected through manual valves I5 and I6 to the pipe II which leads to a float controlled valve I8 in the separating tank l2. When the valve I5 is' closed the mixing tank I3 may be used for permitting the mixed ingredients of the separating medium to age. During the aging period the other tank I4 may be used for storing the previously aged mixture so that when the valve I5 is opened, flow will take place automatically from the. tank I4 to the separating tank I2 under the control of the float valve I8. Consequently, during the operation of the cleaning and washing mechanism illustrated in Fig. 3, the separating medium carried out from the separating tank I2 by removal of the coal and impurities, will be automatically replenished under the control of the float valve I8. When the valve I6 is closed and the valve I5 is opened the flow will be from the tank I3 into the tank I2.

In Fig. 8 I have shown the relative elevations pivot 82 to cause the enclosed mercury switch 83 to connect the conductors 88 and 85 whereupon the solenoid" will be energized since it I the motor switch 88. The motor 85 will then be into the tank I5. When the waterin the tank I5" reaches the level indicated by the dotted line position 93 in Fig. 9, the float 8| will be moved to. its dotted line position 8| to efiect opening of the switch I8 which will cause de-energization of thesolenoid 86 andthe dropping of the "switch 88 to its dotted line position, thereby cut-' ting off the motor 65 and stopping the .pump 84. The operation of the valves 58, 55, 56, 62, 63, 66, and 61, in the system shown in Fig. 8, will be the same as described in connection with Fig. 6. The separating tank I2 in Fig. 8 is provided with a drain valve 94. This valve is opened only when it is-desired to drain the separating tank I2.

By referring to Fig. 3 it will be seenthat the tank 95 is provided for containing water into which the raw coal or run of mine coal may be introduced from the chute 86. By means of the conveyor!" the wetted coal is removed fromthe tank 95 tothe chute 88 for flow into the separating tank I2. The impurities which sink in the separating medium in the tank I2 are removed by means of the travelingconveyor I8 to the chute 2I' and thence to the belt conveyor 88. The motor 31' may be connected by means of the sprocket chain 38 to all of the conveyors in the whole system shown in Fig. 3. The sprocket chain should be driven in the direction of the arrows I88.-

The bottom of the tank 85 is preferably conical in shape and is provided with -a draining port IIII which is connected to the pipe I82 shown in Fig. 8. The draining of the tank 85 may be conwhen the water in the tank 85 becomes con-' taminated with coal dust it may be drained by opening the valve I83-and permitting the sediment to flow intoone of the settling tanks 68 or 6I. It may also occur in practicethat the raw coal introduced into the tank 85 even after screening and de-dusting, has considerable sand and clay adhering thereto which will be washed off by being introduced into the tank 85 and the washed raw coalmay be conveyed out of the I86, I81 inthe direction of the arrows I08, I88 to take the sediment from the inclined bottoms,

*III), III to the chutes H2,- Il3,'*for flow into the mixing tanks I8, I4. The motors I86,'I8l are connected by the sprocket chain gearing H4, I I 5 to the conveyors I84, I85 to drive the same in the direction of the arrows I88, I88. It should be understood, however, that the conveyors I84, I85

are operated alternately because one of the settling tanks receives the sediment from thewashing tanks while sedimentation is taking place in the other sedimentation tank. The coal dust which may be mixed with the clay and sand can readily be separated therefrom by flotation on a liquid separating medium, and the clay and sand recoveredin this manner may be re-used'in the mixing tanks I3 and I4.

* In the co-pending application of applicant and Samuel H. Yost for an Improvement in method of cleaning coal and fluid-separating'mediums therefor, Serial No. 747,906, filed Oct. 11, 1934, the preferred separating medium for use in the tank I2 or tank I2 is described and claimed, whereas the present application adds the preliminary step of wetting the raw coal in the tank 85 and also includes the washing of the separated coal after leaving the separating tank, and in addition I have disclosed in Figs. 4, 6, 8, and 9 systems of handling the liquids and solid materials immersed therein. I, have also added the curve shown in Fig. .10 to illustrate the tests which may be carried outso as to reduce to a minimum the amount of solid constituents carried out from the separating medium when the cleaned coal and the impurities are removed from the tank l2 or tank I2.

In the first place it should be understood that the principal object of wetting the raw coal preliminarily in the tank 85 is to fill up the crevices therein so that less of the solid constituents of the separating medium in the tank I2 will adhere to the separated coal and impurities when they areremoved from the tank I2. Inasmuch as the washing system herein disclosed is arranged and operated to obtain the greatest efficiency, the operating medium is so composed as to retain the greatest amount possible of its solid constituents by preventing the removed coal and impurities from carrying out any more than is necessary. In order to fully understand the significance of the curve shown in Fig. 10, it will be necessary to describe the preparation of the separating medium used in the tank I2 in the system shown in Figs. 1, 2. 5, and 6, and in thetank I2 in the system shown in Figs. 3, 4, and 8. In order to predetermine. the specific gravity of the separating medium or mixture to be used in the systems disclosed in the accompanying drawings, the raw coal or run of mine coal to be cleaned is analyzed by methods of sampling, sink and float tests, l chemical analyses, etc. Then, depending upon what grade of purity of coal is desired, the specific gravity at which separation should take place, when following my improved methods,-is predetermined. The separating medium 'orinixture is then .prepared so that the marketable coal will float in the separating tank I2 or the separating tank I2.

In preparing the separating medium it is preferred to follow certain definite formulae which from actual tests have given the best results but which may be varied in accordance with conditions. By using one part natural clay and four parts natural sand, by weight, without pulverizing or comminuting either the clay or the sand,

and stirring the clay and sand in water, a mesilicate to the mixture of natural clay and natural sand in the water, will cause the clay and sand after being stirred in the water. to remain in suspension for a relatively long period of time,

it is therefore desirable to reduce the agitation to a minimum. For instance, when the agitation of the liquid medium is too great, small and fiat pieces of slate will follow upward currents and be mixed with the cleaned coal, thereby rendering perfect separation impossible. However, in the use of the conveyors l8 and 23 in the'separating tank II or the conveyors II and 23' in the tank l2, the agitation of the liquid medium is so small as not to disturb'the desired separation of impurities from the marketable coal.

If suflicient natural clay is so mixed with water as to finely divide it without comminution or pulverization, a liquid medium may be obtained of sumcient specific gravity to float coal, but it will be found to be too thick or viscous for practical use. However, by adding the proper amount of electrolyte such as sodium aluminate or sodium silicate, the mixture will be rendered more fluid without affecting the specific gravity. After testing various forms of natural clay, one form of fireclay was found that could be used in practice without the addition of sand, but this separating medium was not found to be very emcient. In other words, while satisfactory reseparating process as compared with the speed of operation when natural sand is included in the mixture, because the inclusion of the sand increases the fluidity of the separating medium. Clay is an argillaceous material which is composed of particles in a finely divided state which when mixed with water may be dispersed throughout the volume thereof, while sand is a non-argillaceous granular material usually found in its natural state as silica. The particles of clay in their natural state are relatively fine and the granules of the natural sand are relatively 'coarse. Both of these materials are available at low cost'almost anywhere in this country, and by reason of the use of the electrolyte, preferably sodium aluminate or sodium silicate, no grinding or pulverizing of either the natural clay or the natural sand is necessary in the formation of the separating medium used in my systems illustrated in the accompanying drawlugs.-

The sodium aluminate or sodium silicate may be a de-fiocculating agent so far as the clay suspension is concerned, but the suspension of the sand may perhaps be best explained by the fact that the sodium silicate or sodium aluminate acts as an electrolyte to produce electrical charges in the .clay particles to hold in suspension for a relatively long period of time the natural sand granules in intimate relation with thedispersed clay in a homogeneous separating medium.

In the formation of the separating medium by mixture of the ingredients in the mixing tanks I! and ll of Figs. 4 and 8, .or in the mixing tank 8! of Fig. 6, it is important to follow certain definite formulae according to conditions. It has been found from actual tests that under certain conditions the amount of sodium silicate or sodium aluminate for the best results in maintaining the clay and sand in suspension for a relatively long period of time without agitation, should be approximately .8% of the weight or the clay. By means of tests hereinafter explained the critical proportions may be ascertained. That these proportions are critical is evidenced by the fact that in the tests referred to above. doubling the amount of the electrolyte caused a rapid settling of the clay and sand in a mixed mass without layering.

In order to explain the procedure by which certain definite formulae may be arrived at for ob taining the best results in the use of a separating medium for the cleaning of coal, certain actual tests have been carried out and the results observed. By mixing one part Minford silt (argillaceous material in its natural state) and four parts of white coarse sand by weight, and adding sufiicient water to obtain a specific gravity of 1.55, after stirring into the mixture .8% of sodium. aluminate, no sediment of the solid insoluble ingredients was shown after a period of twenty-four hours.

When a mixture having a specific gravity oi. 1.55 was made of one part Minford silt and five parts sand and .8% of sodium aluminate in water, a very slight settlingwas observed after a lapse of twenty-four hours, but in similar mixtures having one part silt and six parts sand, and one part silt and seven parts sand, pronounced settling occurred after a lapse of twentyfour hours, but the settled mass was a very soft intermixture of silt and sand such as not to interfere with the restarting of the conveyor mechanism shown in the separating tank l2 in Fig. 1 or in the separating tank l2 in Fig. 3. Upon restarting the conveyor mechanism through such settled mass, only a slight mechanical agitation was necessary to recondition the separating medium, but the homogeneous condition of the medium could be obtained only by suflicient agitation. The water used in the foregoing tests was that from a city hydrant in Columbus, Ohio.

When Sandusky Foundry sand (10% clay) was used in tests with Minford silt, there appeared to be no appreciable settling aftera lapse of twentyfour hours, even when the ratio of the ingredients was one part silt to 8 parts of sand, by weight.

Fireclay and white sand mixtures did not prove to be as suitable as silt and white sand mixtures. Fireclay and Sandusky sand mixtures showed no appreciable settling after standing twenty-four hours at a ratio including one part flreclay to six parts Sandusky sand.

Inasmuch as it consumes some time for the progressive deflocculating action of the sodium aluminate to take place, it is preferred to age the mixture for a period of at least twenty-four hours. This can readily be done in the systems shown in Figs. 4\and 8 where two mixing tanks are included for alternate use. When the Minford silt is used with a mixture containing city water, it was found that the minimum deflocculation was effected by the use of sodium aluminate over a, range of .6% to .9% as to the amount of sodium aluminate relative to the weight of the clay. After aging the mixture in the tank 13 or ence in the size of the particles in the two clays.

The Minford silt is the better suspending agent of the two clays tested and the Sandusky sand, a relatively fine sand, is the onemore readily maintained in suspension of the two sands tested.

The permissible sand variation for a given I specific gravitybetween, 1.5 and 1.6 was found to be percent for practical operations. With the less favorable sand, the permissible electrolyte variation plus or minus from the optimum point of .8 percent was found to be 12 percent. .That is to say, the best results are obtained with .8 percent of electrolyte with a permissible range from .6 percent to nearly. one percent.

Inasmuch as Minford silt is composed of finely divided particles of argillaceous material and Sandusky Foundry sand is relatively fine, eight parts of sand could be held in suspension in the water having in solution a small. quantity of sodium aluminate, so that there would be no appreciable settling after a lapse of twenty-fourhours. The highest specific gravity of the mixture can-therefore be obtained when the argillaceous material is in a naturally finely divided state and the sand is relatively fine.

Bentonite is another form of argillaceous material which is found in nature in a finely divided state and has the property of cooperating with an electrolyte to hold tenpart's offine sand in suspension in a separating'medium over a relatively long period of time without agitation.

Fireclay is composed of particles in a finely divided state but not as fine as either silt or bentonite. However, fireclay was found to coact with the electrolyte to hold in suspension six parts of Sandusky sand by weight in a suitable separating medium because no appreciable settling occurredafter standing for twenty-four hours.

- It will thus be seen that the tests which were conducted showed that the selection of the finest argillaceous material in its natural state and the selection, of the finest sand in its natural state enabled the electrolyte sodium aluminate to act to ,hold in suspension the greatest amount of solid ingredients in the separating medium over a long period'of time without appreciable settling, thereby demonstrating the practicability of avoiding agitation although solid insoluble ingredients are used as found in nature without comminution or pulverization. In this manner a separating medium of relatively high specific gravity may be obtained. Such separating medium would have maximum buoyancy and would permit the adding of more water-to obtain the desired specific gravity of'the mixture. Therefore the finer the solid materials the greater may be the fluidity for a given specific gravity.

However, it was found from actual tests that the finer the solid ingredients in theseparating medium the greater would be the carry-off of such materials with the separated coal and with the impurities separated and removed. For instance, the minimum carry-oil of solid ingredients from a separating medium composed of a silt and Sandusky sand (1 part silt plus 4 parts Sandusky'sand'by weight) in water having, in solution .8% sodium aluminate (the separating medium having the specific gravity of 1.53) was about 40 pounds per ton of raw coal treated,

I whereas with a separating medium having a specific gravity of 1.53 and composed of 1 part silt and 4 parts white coarse sand in water having insolutlon .8% sodium aluminate, the carry-01f was found to be 26 lbs. per ton of raw coal treated. Even fireclay gave better results when mixed with coarse white sand than when mixed with the fine Sandusky sand. With a separating medium having the specific gravity of 1.53 and composed of 1 part fireclay and 6 parts white sand by weight in water having in solution .8% sodium aluminate the carry-off was found to be 18 lbs. of solid ingredients per ton'of raw coal treated, whereas with a separating medium composed of 1 part fireclay and 6 parts Sandusky sand by weight in waterhaving in solution .8% sodium aluminate the carry-off was found to be 20 lbs. of -ingredients per ton of raw coal treated.

While therefore theoretically it may be dedivided condition, itis more practical and eco-' nomical to have one relatively fine as found in nature and the other relatively coarse and also as found in nature.

Ageing of the mixture of sodium aluminate, water, clay and-sand greatly reduces the amount of carry-off in the treatment of coal to separate the impurities therefrom. The proper balance may readily be obtained in practice. Fireclaywhite sand mixtures over a' range of M; to A; all

settled considerably faster than silt-white sand mixtures. But fireclay-Sandusky sand mixtures showed no appreciable settling at ratios up to and including Inasmuch as the argillaceous material and the sand varies in nature in various parts of the country the correct formula for the separating medium to suit conditions depends upon the clay suspension, the sandsuspension, and the claysand adherence resulting from contact with smooth imporous surfaces. The related determinations to be made are (1) the concentration of the electrolyte such as sodium aluminate or sirable to have both of the ingredients in finely I 5 sodium silicate to clay which produces the maxi- I mum deflocculation of the clay, (2) the eifect of varying the sand-clay ratios upon the duration of the suspension and the homogeneity of the suspended mixture, (3) the effectof .varying maintain suspension of both ingredients over such a length of time asto render agitation unnecessary, and which will result ina minimum v carry-off of the solid ingredientsclay and sand-from the separating medium. The clay and sand should be available as found in nature without screening or comminution or pulverization, and therefore the process may be carried out anywhere at a very low cost in materials and maintenance. Such sand, of course, includes silica sand. Where solid materials are to be used as sand, by crushing ganister, quartz, etc., the granules need be no smaller than those of ordinary silica sand.

The conclusions from the actual tests made are as to the solid insoluble ingredients, that Sandusky sand, a relatively fine sand, is not as suspension becomes a controllingfactor and re- "favorable as coarser sands unless the matter of i quires its use at lower specific gravities. In other words, the colloidal clay acted upon by the electrolyte has the property of keeping in suspension for a long period of time the finer sands. The tests also showed that silt gave more iavorable results than flreclay. Silt in its natural state is composed of particles more finely divided than the flreclay. The ageing of the mixture for a period of at least twenty-four hours enabled better results to be obtained. I The variation of the specific gravity of the mixture can be controlled by varying the proportion of the water. The

fluidity of each of the mixtures tested was sufli' cient to permit ireesettling of the impurities during flotation of the cleaned coal, since the consistency or mobility of the mixture is not such as to interfere with the rapid operation of the separating process.

It has been found from actual tests that sodium silicate is preferable when the water is well water or hard water, while sodium aluminate is preferable for the'hydrant water of the city of Columbus, Ohio, which water has been treated chemically to purify the same. However, either sodium silicate or sodium aluminate may be used as the suspension agent in either hard water or soft water.

Sodium silicate is usually obtainable in liquid form, whereas sodium aluminate is in powdered or desiccated form, the latter being more conveniently handled than liquid sodium silicate. Both sodium silicate and sodium aluminate can be obtained at very low cost. For instance, in the formula. using one part natural clay and four parts natural sand with .8% of sodium aluminate, the cost of the latter in certain localities is only about 1/250th oi the cost of the clay and sand combined. That is to say, in a separating medium having one part clay, four parts sand and .8 percent sodium aluminate, the cost of the sodium aluminate required is only percent of the cost of the clay and sand combined. This cost of the electrolyte is so low that no attempt need be made in practice to reclaim any of it that clings to the cleaned coal as it passes through the washing tanks shown in the accompanying drawing's.

The formula for making up the mixture or'separatlng medium used in our method of cleaning coal difi'ers with the materials available to serve as the insoluble solid ingredients. The clays which are useful in my method, while having the general characteristics of kaolinite are not necessarily pure clays but would fall under the general classification of shale, surfaces lay, silt and fireclay. These types are widely distributed and readily available in various parts of this country, and each is useful in the process in its natural state. i

The essential characteristics of the argillaceous material in the method of separating coal from its impurities, are those having the property oi being dispersed ordeflccculated bythe electrolyte and after being dispersed or deflocculated,

having the property of maintaining in suspension I the desired quantities of sand or other inert granular material.

Such properties in my separating'medium used in my improved method of cleaning coal, may be readily determined by simple tests which may be carried out wherever clay and sand are found in various parts of the country or wherever it is desired to iollow such method. I have set forth formulae for most emcient operation in certain localities but such formulae may be varied in various parts of the country in accordance with the nature of the natural clays and the natural sands available. I will therefore set forth the procedure that should be adopted to arrive at the most efilcient results for various kinds of clays and sands. g

The procedure is to mix the clay and water to be used, the weight of the clay being about 25 percent of that of the water. This mixture is placed in a series of beakers and to each beaker is added a different amount. of electrolyte such as sodium aluminate or sodium silicate. After the mixture in each beaker is stirred it is allowed to stand for forty-eight hours and the one that shows the best suspension of clay is the mixture that should be selected. If the clay cannot be maintained in suspension in any of the beakers it is not a suitable form of clay.

When a suitable clay is found by following the tests with the electrolyte, the mixture of clay and electrolyte is introduced into a series of beakers, and sand in various proportions is added to the various beakers. The combined weight of the sand and clay should be the same in each beaker. One beaker may contain clay alone and the other one part clay-and two parts sand, one part clay and three parts sand, etc. Some clays such as bentonite, have the property of carrying ten parts of sand when the electrolyte sodium aluminate is used in a suitable separating medium in my method of cle'anlng coal, It should also be understood that sufllcient water is added to the various beakers to obtain the specific gravity required for the desired coal separation.

After the mixtures in the beakers containing the sand have stood for twenty-four hours, observations are made and those beakers eliminated which show settling of the sand at the bottoms of the beakers.

After selecting the most efiicient mixture by proceeding with the tests outlined, the next test to be made is to determine the amount of the mixture that will be carried away with the coal when removed from the separating tank to the first washing tank. For this purpose a piece of polished glass triangular in shape and having sides each four inches long may be dipped into the mixture and withdrawn; by weighing the glass before dipping and after, the weight of the I mixture that adheres to the glass can be calculated. The mixture that carries ed the least amount of separating medium is the most desirable to he used in practice. For instance, in actual tests it was found that for each one-tenth of a rain per square inch carried off by the testing glass, there will be seventeen (17) pounds of mixture carried off by a ton of separated coal.

These tests were made by dipping the glass plate into the beaker mixtures andv weighing while wet. The weights were calculated as the weight of the mixture adhering to each square inch of surface of the plate. Instead of using glass plates imporous card-board squares may be used for immersion in the beaker mixtures but it will be found that less solid material will adhere to the card-board than to the glass plate.

In such carry-off tests of beaker mixtures, a curve maybe plotted from the results obtained. For instance, in connection with actual tests made with a series of beaker mixtures in which the amount of sodium silicate ranged from zero to 3.6 percent by weight of clay in the fluid, the plotted curve will show a gradual decrease in the amount of clay carried out on a card until the percentage of sodium silicate is about 1.3

or 1.4,.aiter which the increase of the percentage of sodiuinsilicate vinoreasesthe amount of clay carried out on a card. The clay used was a form of' fireclay having a pH value of 5.

twenty-four hours after adding the electrolyte and stirring the mixture, it was found that the clay remained in suspension the longest in the beaker having 1% of sodium silicate by weight 01- clay in the'mixture, and the tests further showed that the range for best results would be between 1% and 1.4 of electrolyte. The carry-off tests of clay mixtures also enabled the plotted curve in Fig. 10 to show pounds of clay per ton of coal that would be carried out of the medium during the coal separating process. For instance, in

the tests just described where the best results would be obtained with the electrolyte 1.3% by weight of clay in the mixture, the least amount of clay would be carried out on the card and would represent about pounds of clay per ton of coal.

As above explained, there is a permissible range in the use of the proportions of the ingredients in the water for maintenance of the clay and "sand in suspension over relatively long periods should be understood that during the operation of the separating apparatus the intermixture of the ingredients is so thorough that when the cleaned coal and impurities are removed from the separation tank, the medium that clings to the removed materials is about the same in its proportions of constituents as the medium that remains in the tank. The medium in the tank therefore remains as to specific gravity and emciency, the same as when first introduced and the replenishment of the medium in the separating tank is by means of the same'mixture as that selected by means of the foregoing tests.

Inasmuch as it is important to reduce to a minimum the amount of solid ingredientscarried oil from the separating medium and it is also important to maintain suspension of the solid ingredients in the separatingmedium, the curve shown in Fig. 10 after.being plotted from the tests above outlined, may be used to determine the most practical percentage of sodium silicate or sodium aluminate in the separating medium. For instance, since the best results from the tests indicate from .6% to .9% of sodium silicate by weight of clay and the curve shown in Fig. 10 indicates 1.3% of sodium silicate by weight of clay, approximately one percent of sodium silicate by weight of clay' could be used in practice critical as above explained, the region to the left of the lowest point of the curve of Fig. 10 should be relied on to determinelthe percentage of elec- After permitting the beaker mixtures to stand for suspension of the solid ingredients in the separating medium andas to reduction to. the minimum of the solid ingredients carried oil from the separating medium.

It should be particularly noted by reference to Figs. 4, 8, and 9 that the operation of separating coal from the impurities may be carried on automatically over an extended period of time, For instance, if the tank 13 acts as a storage tank while :the valve 16 is closed and the valve 15 open, the automatic float valve I8 will maintain the depth of the separating medium in the separating tank I! at a predetermined level. At the same time the settling tank 60 may have clear liquid therein so that when the valve 66 is closed and the valve 61 is open the float controlled switch I! will efleot intermittent automatic operation oi the pump 64 to replenish water in the tank ii for flow successively into the tanks i4, and It. This is true whether the valve 54 is open or not but will take place oftener if the valve 54 is partially open and the valve 62 is closed when the valve 63 is open. There will then be a con tinuous draining of settling material from the bottom of the tank l3 to the settling tank 6! while the automatically controlled and operated motor M replenishes the water in the tanks 15', II and i3. When sediment is removed from either of the settling tanks 60 or 6| it may be delivered by means of the chutes H2, H3 directly to the mixing tanks 13, ll, as shown in Fig. 7.

That is to say, when the system shown in-Fig. 4

is in operation, the valve 94 is keptopen continuously. The extent of opening of the valve 94 is regulated so that the water in the last tank i5 is practically clear. If the water in the second tank I4 is practically clear, too much water is being used in the automatic circulating system which indicates that the valve 9| should be parratus' used in my system and for my methods the liquids are substantially quiescent. This is particularly true in the separating tank the bottom of which is entirely closed during operation and in which no special means is provided for agitating the separating medium. The conveyors for removing the separated coal and impurities are operated at a relatively slow speed and may be arranged either as shown in-Fig, 1 or as shown in Fig. 3.

While I prefer to include the preliminary wetting of the raw coal for the reasons hereinbefore explained this is not always necessary or desirable .from the standpoint of economic operation. -The raw coal wet or dry, is fed into a quiet pool or separating bath in the separating tank and .the separated coal is then moved up ing tank to said sedimentation tank, and autohowever, it may still be economical to retain the water circulation for the washing tanks. That is, the sedimentation steps may be carried out for the purpose of obtaining clear water to replenish that usedin the washing tanks and this may be done automatically. In fact, all of the apparatus shown in the drawings may be retained if desired, although the sediment from the sedimentation tanks is discarded.

Obviously those skilled in the art may make various changes in the details and arrangement of parts without departing from the spirit and scope of the invention as defined by the claims hereto appended, and I therefore wish not to be restricted to the precise construction herein disclosed,

Having thus described and shown an embodiment of my invention, what I desire to secure'by Letters Patent of the United States is:

1. In apparatus for separating coal from its impurities, and washing the separated coal. the combination with a wetting tank, of a separating tank, a washing tank, two sedimentation reclaiming tanks adapted to be used alternately, two mixing and storage tanks either adapted to be used as a mixing tank while the other is being used as a storage tank, means connected between the lastnamed tanks and said separating tank to maintain the separating medium in the last-named tank at a predetermined level, means afiording flow of settled solids from the washing tank to either of said sedimentation tanks, automatic mechanism for pumping water from either sedimentation tank to said washing tank to maintain the depth of water in the latter at a predetermined level, and conveyor mechanism associated with the separating tank for removing impurities and separated coal therefrom, and conveyor mechanism for the washing tank to remove the washed coal therefrom.

2. In apparatus for separating coal from its impurities, the combination with a separating tank, of a washing tank, a sedimentation tank. conveyor mechanism for removing separately the separated coal and impurities from the separating tank, conveyor mechanism for removing separated coal from the washing tank, means for effecting transfer of settled solids from the washmatic pump mechanism for pumping water from the sedimentation tank into said washing tank to maintain the depth in the latter at a predetermined level.

3. The method of cleaning coal which comprises mixing a separating, medium comprising insoluble granular material and a deflocculating or dispersion agent, storing and aging said medium, introducing said separating medium into a separating tank, introducing raw coal into said.

separating medium while in a quiescent condition insaid separating tank thereby separating the coal from the refuse, removing the refuse from said tank, removing the coal from said tank while leaving the separating medium therein except for particles which adhere to said coal, washing said coal to remove the adhering separating medium therefrom, and recovering the removed separating medium to be used again."

4. The method of cleaning coal which comprises mixing a separating medium comprising insoluble granular matriahclay, and a defloccnlating or dispersion agent, storing and aging said medium, introducing said separating medium into a separating tank, introducing raw coal into said separating medium while in said separating tank thereby separating the coal from the refuse, removing the refuse from said tank, removing the coal from said tank while leaving the separating medium therein except for particles which adhere to said coal, washing said coal to remove the adhering separating medium therefrom, and recovering the removed separating medium to be used again.

5. The method of cleaning coal which comprises mixing a. separating medium comprising sand, clay and a deflocculating or dispersion agent, storing and aging said medium, introducing said separating medium into a separating tank, introducing raw coal into said separating medium while in a quiescent condition in said separating tank thereby separating the coal from the refuse, removing the refuse from said tank, removing the coal from said tank while leaving the separating medium therein except for particles which adhere to said coal, washing said coal to remove the adhering separating medium therefrom, and recovering the removed separating medium to be used again. I

6. The method of cleaning coal which comprises mixing a separating medium comprising clay, sand and a relatively small amount of a defiocculating or dispersion agent, storing and aging said medium in a quiescent state, introducing said aged separating medium into a separating tank, introducing raw coal into said tank. and separately removing the materials which float and those which sink.

7. The method of cleaning coal which comprises mixing a separating medium comprising sand and a relatively small amount of a defiocculating or dispersion agent, storing and aging said medium in a quiescent state, introducing said aged separating medium into a separating tank, introducing raw coal into said tank, and separately removing the materials which float and those which sink.

8. The method of cleaning coal which comprises mixing a separating medium comprising clay and a relatively small amount of a deflocculating or dispersion agent, storing and aging said medium in a quiescent state, introducing said aged separating medium into a separating tank, introducing raw coal into said tank, and separately removing the materials which float and those which sink.

9. In a systern ol separating impurities from raw coal, the combination with a separating tank, of means comprising a float controlled valve for maintaining the depth of separating medium in said tank at a predetermined level, a washing tank, a settling tank, means for controlling draining of sediment from said washing tank to said settling tank, means comprising a pump for drawing liquid from above the sediment in said settling tank and. delivering said liquid to said washing tank, a motor for operating said pump, automatic means comprising a float in said washing tank for controlling said motor to operatesaid pump to maintain the depth of liquid in said washing tank at a predetermined level, means for removing separated impurities from said separating tank, and means for moving cleaned coal from said separating tank into said washing tank and then out of the latter.

10. In a system of separating impurities from raw coal, the combination with a wetting tank adapted to contain water, of a separating tank adapted to contain aseparating medium, means for introducing raw coal into the water in the wetting tank and then deliver such wetted coal into the medium in said separating tank, a washing tank adapted to contain water, means for removing the separated impurities from said separating 'tank, means for removing cleaned coal from said separating tank and moving it into and out of the water in-said washing tank, a settling tank, means for eifecting drainage of sediment from said wetting and washing tanks into said settlement tank, and automatic means for drawing water from above the sediment in said settling tank and introducing such water into said washing tank to maintain the depth of water in the latter at a predetermined level.

11. In a system of separating impurities from raw coai, the combination with a separating tank adapted to contain a separating medium comprising granular material held in suspension by a dispersion agent, means for removing from said tank the separated impurities, a settling tank, means comprising a valve for controlling drainage to said settling tank of impurities settled to the bottom of said separating tank, a washing tank adapted to contain water, means for removing cleaned coal from said separating tank andmoving such cleaned coal into and out of the water in said washing tank, means comprising a valve for controlling drainage of sediment from said washing tank into said settling tank, and automatic means for-controlling the drawing of 1 liquid from above the sediment in said settling tank and introducing said liquid into said washing tank to maintain the depth in the latter at a predetermined level.

12. In a system of separating impurities from raw coal, the combination with a separating tank adapted to contain a separating medium, of a plurality of washing tanks each adapted to contain water, overflow means between each washing tank and the next adjacent washing tank, mechanism for removing separated impurities from said separating tank, a settling tank, means for controlling flow of sediment from said washing tanks to said settling tank, means for removing cleaned coal from said separating tank and then moving such cleaned coal intoand out of the water successively in said washing tanks, and automatic means for drawing water-from above the sediment in the settling tank and introducing such water into one of said washing tanks to the level of said overflow means to efiect auniiorm predetermined depth in all of-the washing tanks.

Nils D. LEVIN. 

